Wednesday, February 8, 2017

Cotton Variety Selection: More Bt Traits to Choose From

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service

Variety selection is the most important decision made during the year. Selecting Bt vs non-Bt or the kind of insect trait package is an important consideration in selecting cotton varieties.
Bt cotton is genetically altered to produce certain proteins which are toxic to specific groups of insects. For example, currently available Bt traits in cotton specifically target worm pests such as cotton bollworm, tobacco budworm, and beet armyworm. On the other hand, conventional, or non-Bt cotton does not produce such insecticidal proteins and as a result it is more vulnerable to worm damage.

Since the introduction of Bt cotton into US agriculture in 1996, the technology has transformed from a single-gene trait to multi-gene trait packages. The 1st generation Bt cotton had only a single Bt gene. The second generation Bt technologies, such as Bollgard 2, TwinLink, and WideStrike produce two Bt toxins. While the most recent 3rd generation Bt is a three-gene trait—Phytogen brand varieties with WideStrike 3 have already been in the market for the last couple of seasons. Recently, Monsanto (Deltapine brand) and Bayer CropScience (FiberMax and Stoneville brands) announced the availability of some of their varieties with Bollgard 3 and TwinLink Plus technologies, respectively.

Bt Technologies
Proteins expressed
Second generation

Bollgard 2
Cry1Ac + Cry2Ab
Cry1Ac + Cry1F
Cry1Ab + Cry2Ae
Third generation

WideStrike 3
Cry1F + Cry1Ac + Vip3A
Bollgard 3
Cry1Ac + Cry2Ab + Vip3A
TwinLink Plus
Cry1Ab + Cry2Ae + Vip3Aa19

Over the years, Bt technologies have been fairly effective controlling worms in cotton. The second generation Bt was more effective than the first one, and the third generation technology is more effective than the second generation due to the addition of toxin(s). Newer traits usually come with additional costs, so if you don’t need these traits, varieties with older trait packages are still competitive in yield and quality.

Some farmers may choose to go with non-Bt cotton to avoid paying tech fees. With non-Bt cotton, field scouting becomes even more important to stay on top of the game. In 2016, worm pressure on the Texas High Plains was so low that many of our non-Bt cotton fields got away without spraying for worms. This doesn’t mean we will have a similar situation in 2017---we may face higher worm pressure—therefore, there is higher risk associated with the non-Bt crop compared to Bt. However, with a good scouting program in place and timely insecticide applications, non-Bt cotton can perform well.

Finally, insect trait is an important consideration in selecting varieties but it should not take priority over agronomic characteristics such as yield, maturity, and fiber quality. I have seen some of the non-Bt cotton varieties performing as well as Bt cotton and sometimes even better (especially on the Texas High Plains where worm pressure is usually light). Therefore, it’s not the transgenic insect trait but the inherent yield potential of a variety which should come first in the decision making.